The present invention relates to mounting supports for pollution control devices, and more particularly to a sheet of mounting material suitable for wrapping a pollution control element of a pollution control device, and even more particularly to a sheet of mounting material having mating edges that form a seam at a non-perpendicular angle to the inlet and outlet of the pollution control element in a pollution control device.
Pollution control devices are employed on motor vehicles to control atmospheric pollution. Catalytic converters and diesel particulate filters are two types of pollution control devices which are currently in widespread use. Both of these devices typically contain a monolithic structure mounted within a metal housing with a mounting material disposed between the structure and the walls of the housing. The monolithic structure, or monolith, is either made from metal or more commonly, a ceramic material.
Ceramic monoliths generally have very thin walls and are susceptible to breakage. Typically, a ceramic monolith has a coefficient of thermal expansion about an order of magnitude less than the metal housing in which it is contained. To avoid damage to the ceramic monolith from road shock and vibration, to compensate for the differences in thermal expansion of the monolith and housing, and to prevent exhaust gases from flowing between the monolith and metal housing, mounting materials are typically disposed between the ceramic monolith and the metal housing.
The mounting materials are generally manufactured in sheet form from ceramic fibrous materials. Pollution control devices employing mounting materials generally use a single sheet or mat with mating edges having either a tongue and groove configuration or a half lap configuration. The tongue and groove configuration includes a slot on one end of a mating edge and a tab on the opposing mating edge. The half lap configuration includes a tab on one half of the mating edge that corresponds to a slot on one half of an opposing mating edge. The sheet or mat is wrapped around the outer surface, or face, of the ceramic monolith with either the tongue and groove or half lap configuration engaged to form a seam in the mat. With either configuration, the tab must fit exactly into the slot to ensure a tight gas seal about the periphery of the ceramic monolith.
The diameter of individual ceramic monoliths will generally vary from a desired standard due to manufacturing constraints. Therefore, the circumference, or perimeter, of the monolith will also vary. This variance in monolith diameter means that the mat will tend to be either too long or too short as the individual ceramic monolith varies. An overlap of the mat can cause improper closure of the housing with the attendant risk of mounting failure or crushing of the ceramic monolith. An overlap is usually avoided by designing the mat length for a monolith having the minimum perimeter. This ensures that mat overlap will never occur, but it also means that the mat will often be too short and leave a space or gap where the two ends of the mat should come together. This space is undesirable because it provides an additional edge area on the mat for the exhaust gas to impinge upon. The open space may cause erosion or degradation of the insulating material, particularly at an exposed tab that is perpendicular to the flow of the gas stream. This space also allows a greater amount of heat to be conducted to the metal housing because hot exhaust gases come into direct contact with the metal housing and can eventually damage the housing.
Thus, existing techniques utilized for securing a mounting mat about an outer surface of a monolith typically include mating configurations that do not adequately compensate for the variations in diameter of individual monoliths. Additionally, existing techniques for securing the mat about the outer surface of the monolith result in gaps or spaces that expose the securing mechanism in the mounting mat to the direct flow of exhaust gases. The exposure of the securing feature of the mat to exhaust gas streams increases the potential for erosion of the mat and the subsequent failure of the pollution control device.
The present invention provides a pollution control device that includes a mounting material suitable for wrapping a pollution control element and securing the wrapped element within the pollution control device. The present invention is generally utilized in pollution control devices such as catalytic converters and diesel particulate filters.
The pollution control device of the present invention includes a housing and a monolith positioned within the housing. The monolith has an inlet, an outlet, and an outer surface. A sheet of mounting, having opposing mating edges, is positioned around the outer surface of the monolith between the monolith and housing. The sheet of mounting material is positioned such that at least a portion of the mating edges meet to form a seam that is non-perpendicular to the inlet and outlet of the monolith.
The mating edges of the present invention may be provided through several different embodiments. For example, one embodiment of the present invention includes a sheet of mounting material having opposing lateral edges, substantially parallel to each other, and opposing and edges, substantially parallel to each other. The end edges are at a non-perpendicular angle to the lateral edges. The end edges serve as the mating edges for the wrapped configuration. Thus, the mating edges of the mat when wrapped around an outer surface of a pollution control device, meet and form a seam that is non-perpendicular to the inlet and outlet of the pollution control device. Another embodiment of the invention includes the use of lateral edges as mating edges. In this embodiment, an elongated and narrow sheet of material is wrapped around the outer surface of the pollution control device with the lateral edges contacting opposing lateral edges to form a seam that is non-perpendicualr to the inlet and outlet of the pollution control element.
The seam formed by the mating edges of the present invention is at an angle that is non-perpendicular to the inlet and outlet of the pollution control device. This specific configuration enables the adjustment of the sheet of mounting material and reduces the exposure of the mating edge to the direct flow of the exhaust gases.
It is an advantage to utilize a sheet of mounting material that has a configuration that compensates for the size variance in individual monoliths. It is a further advantage to provide a sheet of mounting material that has a seam at a non-perpendicular angle to the flow of exhaust gases to reduce erosion and potential failure of the mounting material as a sealant layer.